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      How to Run A/B Tests on Email Subject Lines in Letterhead

      This article explains how to set up and run an A/B test on email subject lines in your newsletters. A/B testing helps you automatically send the best-performing subject line to most of your audience, boosting open rates and engagement.

      Before You Start

      • You’ll need at least 400 audience members for A/B testing to work.

      • A/B testing is currently available only for email subject lines (not preview text or newsletter content).

      • The feature automatically splits your audience:

        • 25% receives the test (split between two subject lines).

        • 75% receives the winning subject line based on open rates.

      Step-by-Step Instructions

      1. Go to your Newsletter draft.

        • From the left-hand menu, select Newsletters.

        • Choose the draft you’d like to edit.

      2. Proceed to the Preview & Schedule step.

        • Click Continue editing until you reach Step 2: Preview and Schedule.

      3. Enable A/B Testing.

        • Toggle the switch next to Create A/B Test.

      4. Enter your subject lines.

        • In the Email Subject fields, type two different subject line variations you want to test.

      5. Set your send details.

        • Choose your Audience.

        • Pick your Date and Time to send.

        • (Optional) Send a test email before scheduling.

      6. Schedule your newsletter.

        • Click Schedule.

        • Letterhead will send the subject line variations to 25% of your audience, measure open rates, and automatically send the winning subject line to the remaining 75%.

      Reviewing Results

      After your newsletter is sent, you can view the results in the Newsletter Metrics dashboard:

      • See both subject lines with full text.

      • A “winner” badge will mark the best performer.

      • Metrics include:

        • Opens (count)

        • Open Rate (%)

        • Recipients reached

      Troubleshooting / FAQs

      • What happens if my audience is smaller than 400 members?
        A/B testing requires at least 400 recipients. If your audience is smaller, the toggle won’t be available.

      • Can I test more than two subject lines?
        Not at this time. Each test supports two subject line variations.

      • Where can I see past results?
        Go to your Published Newsletter metrics. Each newsletter will display the A/B Test Results section if it includes a test.

        Need Help?

        If you have questions or need assistance, please contact our support team at support@tryletterhead.com or log a support ticket through the Help Center!